There is currently proposed a power conversion device in which a plurality of power conversion units are connected through a common busbar, and supplies power to a load.
Patent Literature 1 discloses a power supply device including a master power-supply unit including a battery, a voltage converter that converts a voltage supplied from the battery of the master power-supply unit, a slave power-supply unit including a battery, a voltage converter that converts a voltage supplied from the battery of the slave power-supply unit, a capacitor that smooths a voltage supplied from each of the two voltage converters, and a sensor that detects a voltage between terminals of the capacitor. When the capacitor is precharged, the power supply device executes control to switch between a relay that switches over the connection state between the capacitor and the battery of the master power-supply unit, and a relay that switches over the connection state between the capacitor and the battery of the slave power-supply unit, based on whether there is a fault in the sensor.
As described above, there is employed DC common-busbar connection in which power-supply-side terminals of a plurality of inverters are connected in parallel and DC-side terminals of the inverters are connected in parallel. A case where two inverters are connected through a DC common busbar is described.
When a power failure occurs, a DC voltage Vdc decreases. At the stage where the DC voltage Vdc decreases to a voltage Vdc1, each of the two inverters executes control to turn off switches of spare charge circuits.
Assuming that the power supply is resumed before the DC voltage Vdc decreases to the voltage Vdc1, each switch of the two inverters is in an on-state. Therefore, a phenomenon occurs, in which a short-circuit charge current flows from the resumed power supply to each of the main-circuit capacitors. A general inverter uses components (such as a converter diode) that can withstand the short-circuit charge current as described above.